People v. Risley, 214 N.Y. 75 (1915)

Evidence based on mathematical probability, particularly when used to establish the improbability of certain events or conditions, is inadmissible when it lacks a foundation in observed data and relies on speculation rather than demonstrable facts.

Summary

Risley, an attorney, was convicted of offering a forged document as evidence. The prosecution presented expert testimony applying mathematical probability to typewriter defects to argue the document was altered on Risley’s machine. The Court of Appeals reversed, holding that such speculative probability evidence, lacking a basis in actual observed data about typewriters and their use, was inadmissible and prejudicial. The ruling underscores the importance of grounding evidence in factual observations rather than theoretical probabilities, especially when expert testimony may unduly influence the jury.

Facts

Risley represented Bennett in a patent dispute against Iron Clad Manufacturing. During a trial in February 1911, Risley offered an affidavit. It was alleged the words “the same” had been fraudulently inserted into the affidavit. The prosecution claimed Risley altered the affidavit to strengthen his client’s case after an appellate court highlighted deficiencies in the evidence. The prosecution presented evidence that Risley had accessed the document at the County Clerk’s office shortly before the trial. Samples of typewriting from Risley’s office typewriter were introduced to demonstrate similarities with the altered document.

Procedural History

Risley was convicted in the trial court for offering a forged document in evidence. The Appellate Division affirmed the conviction. Risley appealed to the New York Court of Appeals.

Issue(s)

Whether the trial court erred in admitting expert testimony based on mathematical probabilities to demonstrate the unlikelihood of the defects in the forged document being produced by a typewriter other than the defendant’s.

Holding

No, because the mathematical probability evidence presented by the prosecution was speculative and lacked a sufficient foundation in observed data, rendering it inadmissible and prejudicial to the defendant.

Court’s Reasoning

The Court of Appeals found the admission of mathematical probability evidence to be reversible error. The Court emphasized that the expert witness (a mathematics professor) lacked specific expertise in typewriters and did not account for the human element in operating the machine. The Court distinguished this type of evidence from actuarial tables, which are based on observed data. The Court stated the witness’s testimony “was not based upon actual observed data, but was simply speculative, and an attempt to make inferences deduced from a general theory in no way connected with the matter under consideration supply the usual method of proof.” The Court noted that the jury might give undue weight to such complex and seemingly scientific evidence, potentially obscuring other important facts. Therefore, the Court concluded that allowing such speculative evidence was prejudicial to the defendant and warranted a new trial.